1. Field of the Invention:
This invention relates to seal arrangements between rotating and stationary members, and in particular, to a seal arrangement which reduces velocity carryover and at the same time is impervious to axial deflections of the rotating member.
2. Description of the Prior Art:
It is well known in the sealing art to utilize a labyrinth seal in order to provide effective sealing between a rotating and a stationary member and to isolate the interior of a casing from the exterior thereof along an interface between the casing and a rotating shaft passing therethrough. It is also well known that such labyrinth seals increase their effectiveness if there is provided some method of preventing or diverting the velocity of a fluid from carrying over from a given labyrinth seal strip to the next axially adjacent seal strip. If such velocity carryover is permitted, a greater leakage of fluid through the entire labyrinth seal arrangement occurs.
Thus, it is common practice to provide deflector strips on one of the adjacent members, usually the rotating member, which are staggered between adjacent axial seal strip rows and which are overlapped radially by the seal strip. For example, in the turbine art, it is well known to provide a labyrinth seal in which the seal strips extend radially inward from the interior of the casing (the stationary member), while the deflector strips are positioned on the rotating member such that the deflectors are axially interspersed between the adjacent axial seal strips. Also the deflector seals extend radially outward from the rotating member for a distance sufficient to have the deflector seals overlapped by the radial dimension of the labyrinth seal strip. Such seal arrangements may be provided in which the deflectors extend radially and terminate along a common datum parallel to the axis of rotation, or else provided such that the deflectors are stepped and proceed at an angle relative to the axis of the rotating shaft.
Such staggered seals have however not been utilized in regions of the apparatus where displacement of the deflector seals may occur, such as displacement resulting from thermal expansion. Thus, for example, it is not common practice in the art to utilize a labyrinth seal strip with associated deflectors in a staggered axial relationship at the extremities of turbine rotor shafts to prevent leakage from the interior of the turbine along the shaft at the point that the shaft passes through the casing. This is so since the rotor may experience "end travel" due to thermal expansion thereof and such end travel would generate abrasion between the deflectors and the radially overlapping labyrinth strips to negate the effectiveness of the seal provided.